I have a friend that sent a email to adsense with a question about blocking URL's. They answered her question and then asked her if she would like to try their BETA testing of keyword blocking for Adsense. I was going to post the quote but don't want to get into trouble for posting a email quote.
"we are currently beta testing a feature that allows publishers to block all ads containing a certain keyword." Then they asked her to reply to the email with a list of keywords to block.